Fill level measurement devices operating in accordance with the radar principle are intended to always provide a clear measurement result. This means that a measurement value within a measurement range can be provided always at a specified degree of accuracy. In the case of large distances, the prediction that the measurement value is greater than a maximum distance or that the measurement value cannot be determined is usually sufficient. In the case of short distances too, i.e. in the region close to the sensor, it is possible that the sensor may not be able to provide a sure identification of the maximum fill level or of the maximum level. In particular, radar sensors known thus far often do not provide a clear signal in the flooded state of the measuring sensor. Said signals may correspond for example to a very distant target, or it is possible for the received signal to be similar to a measurement signal inside an absorber.
In sensors known thus far, archiving functions are often used in order to follow and re-identify targets or echoes. However, since a sure identification is also required the first time the sensor is switched on, these functions cannot be used in the case of ambiguous echo relationships.